Changes in Each Component of Accumulated Other Comprehensive (Loss) Income (Detail) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Jan. 31, 2016		Jan. 31, 2015		Jan. 31, 2016		Jan. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive (loss) income, beginning balance	$ (56,715)		$ (17,671)		$ (40,623)		$ (2,388)
Unrealized (losses) gains arising during the period	(11,447)		(26,542)		(28,434)		(42,779)
Reclassification of realized net losses (gains) to net income	447		466		1,342		1,420
Accumulated other comprehensive (loss)income, ending balance	(67,715)		(43,747)		(67,715)		(43,747)
Accumulated Translation Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive (loss) income, beginning balance	(37,902)		(631)		(20,919)		15,604
Unrealized (losses) gains arising during the period	(11,447)		(26,537)		(28,430)		(42,772)
Accumulated other comprehensive (loss)income, ending balance	(49,349)		(27,168)		(49,349)		(27,168)
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive (loss) income, beginning balance	(18,813)	[1]	(17,052)	[2]	(19,708)	[1]	(18,006)	[2]
Reclassification of realized net losses (gains) to net income	447	[1]	466	[2]	1,342	[1]	1,420	[2]
Accumulated other comprehensive (loss)income, ending balance	$ (18,366)	[1]	(16,586)	[2]	(18,366)	[1]	(16,586)	[2]
Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive (loss) income, beginning balance			12		4		14
Unrealized (losses) gains arising during the period			(5)		$ (4)		(7)
Accumulated other comprehensive (loss)income, ending balance			$ 7				$ 7

[1] The tax effects on the reclassifications of realized net losses was $0.3 million and $0.9 million for the three and nine months ended January 31, 2016, respectively.

[2] The tax effects on the reclassifications of realized net losses was $0.3 million and $0.9 million for the three and nine months ended January 31, 2015, respectively.